1. Field of the Invention
The present invention is related to the manufacture of acrylonitrile by the direct ammoxidation of a saturated hydrocarbon (e.g., propane), ammonia and oxygen in a reactor containing an ammoxidation catalyst. More specifically, the invention is related to the substantial reduction of unreacted ammonia, ammonium salts and resulting waste products produced from the unreacted ammonia. In particular, the invention relates to the addition of C.sub.2 -C.sub.5 olefin to the reactor to react with the unreacted ammonia thereby reducing and/or eliminating unreacted ammonia from the reactor effluent. This substantial reduction of ammonia in the reactor effluent provides significant environmental and economic advantages.
This invention has particular utility in the conversion of existing propylene based feed acrylonitrile plants to propane based feed acrylonitrile plants.
2. Description of the Prior Art
The production of acrylonitrile from propane is an emerging technology. While there are numerous patents related to catalysts and processing schemes for such technology. Commercialization of this technology has not yet occurred and acrylonitrile continues to be produced throughout the world via the ammoxidation of propylene (a more expensive feedstock than propane).
For both the ammoxidation of propylene and propane to acrylonitrile, ammonia is a required feedstock. Typically, unreacted ammonia remains in the reactor effluent, a condition known as "ammonia breakthrough". In order to remove unreacted ammonia in commercial propylene based processes, the reactor effluent is contacted with a sulfuric acid quench to form ammonium sulfate which is then removed from the process as an aqueous waste stream which is then deep-welled or subjected to biological treatment.
In processes for the fluid-bed ammoxidation of propylene to acrylonitrile, U.S. Pat. Nos. 5,288,473 and 5,457,223 teach the substantial reduction of ammonia in the reactor effluent by the strategic addition of an oxygenate compound, preferably methanol, to the reactor.
An object of the present invention is a solution to ammonia breakthrough in processes for the ammoxidation of propane or isobutane to acrylonitrile.
A further object of the instant invention is an economical process scheme for the conversion of a propylene feed acrylonitrile plant to a propane or isobutane feed plant.